JP2002141300A - Laser annealing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laser annealing device for irradiating laser light for forming a thin film of superior crystallinity required for manufacturing the thin-film transistor of high performance, in a laser heating processing method. SOLUTION: A laser optical system is provided with a linear beam forming means, forming a plurality of square laser beams radiated from a plurality of laser oscillators in linear beam shapes on an amorphous or polycrystalline silicon film formed on a substrate. The optical axes of the laser beams from the laser oscillators to the linear beam forming means are substantially on the same plane. The linear beams are arranged substantially linearly on the amorphous or polycrystalline silicon film formed on the substrate at arbitrary intervals. Thus, the laser optical systems of a plurality of linear beam forming means can be arranged at distances, and the interference of optical parts can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a laser heat treatment apparatus for forming a polycrystalline semiconductor film having excellent crystallinity, particularly a silicon film.

[0002]

2. Description of the Related Art A pixel portion of a liquid crystal display forms an image by switching thin film transistors formed on an amorphous or polycrystalline silicon film formed on a glass or synthetic quartz substrate. However, the crystallinity of the silicon film constituting the transistor active layer is low, and the thin film transistor has low performance as typified by mobility, and it is difficult to manufacture an integrated circuit that requires high speed and high functionality. . Therefore, as a method of improving the crystallinity of a silicon film, a laser heat treatment for increasing the crystallinity of a silicon film formed on a substrate is performed as a method of improving the crystallinity of the silicon film in order to realize a high mobility thin film transistor.

A pixel transistor in a pixel portion of a liquid crystal panel is driven by a driver circuit. The driver circuit is mainly independently arranged outside, but realizes high speed and high functionality of a polycrystalline silicon film. If possible, the driver circuit can be simultaneously configured close to the pixel transistor. If this becomes possible, there will be tremendous advantages in terms of the manufacturing cost and reliability of the liquid crystal panel.

[0004] The relationship between the crystallinity of the silicon film and the mobility of the thin film transistor is explained as follows. The silicon film obtained by the laser heat treatment is generally polycrystalline. The polycrystalline grain boundaries are composed of lattice defects, and these defects scatter carriers in the thin film transistor active layer and hinder movement. Therefore, in order to increase the mobility of the thin film transistor, it is important to reduce the frequency at which the active layer of the carrier crosses the crystal grain boundary during the movement, and it is necessary to reduce the lattice defect density. The purpose of the laser heat treatment is to form a polycrystalline silicon film having a large crystal grain size and few lattice defects at crystal grain boundaries from an amorphous silicon film formed on a substrate.

[0005]

The present inventors have proposed an optical system for laser heat treatment in Japanese Patent Application No. 11-179233, which employs an optical system for transmitting a laser beam from a laser oscillator. A linear distribution of the irradiation laser beam on the surface of the silicon film, and the linear beam is swept relatively on the silicon film in a direction perpendicular to the linear beam.

FIGS. 4 and 5 are schematic diagrams of the laser optical system 3. The laser beam 2 emitted from the laser oscillator 1 is applied to an intensity distribution shaping unit 30 and a beam shape shaping unit 3.
1 and irradiates the silicon film 5 deposited on the substrate 50.

The laser beam 2 emitted from the laser oscillator 1 usually shows a Gaussian intensity distribution, but the intensity distribution shaping means 30 operates, for example, while preserving the Gaussian intensity distribution in the x direction of the beam cross section. Only the intensity distribution in the y direction of the cross section is smoothed.

[0008] The laser beam having such a top hat distribution is adjusted by the beam shape shaping means 31 to adjust the magnification of the width of the laser beam in the x direction and the y direction. The beam shape may be rectangular or linear. When the longitudinal direction of the rectangular laser beam is taken in the y direction, the intensity distribution XC in the x direction on the surface C of the silicon film 5 has a shape in which the intensity distribution XA in the x direction on the incident surface A of the intensity distribution shaping means 30 is reduced. Thus, the properties such as the directivity of the oscillation laser light 2 are still preserved, while the intensity distribution YC in the y direction on the upper surface C of the silicon film becomes a substantially uniform distribution.

On the other hand, the object of laser irradiation and the silicon film 5
The substrate 50 is formed on a silicon oxide film formed as a base film 51 on a substrate 50 made of glass or the like. The substrate 50 is fixed to a scanning stage, and moves an irradiated rectangular laser beam in the x direction. While heating, the silicon film is heated by laser irradiation.

When the surface of the silicon film 5 formed on the substrate is irradiated with a rectangular laser beam while sweeping in the x direction,
The silicon film 5 is heated by absorbing the laser beam and melted in a rectangular shape. At this time, a temperature gradient does not occur in the longitudinal direction of the irradiation laser beam, that is, the y direction because the intensity distribution of the laser beam 2 is uniform, but a temperature gradient due to cooling occurs in the x direction, which is the sweep direction. When the melted silicon film is crystallized by cooling, the crystal grows in accordance with the temperature gradient, so that it becomes one-dimensional growth (unidirectional growth) in the moving direction of the substrate 50, that is, in the x direction, and the crystal grain size is about several μm. Are formed along the sweep direction.

When a rectangular or linear beam is used for such laser heat treatment, the intensity distribution in the width direction of the laser beam greatly affects the recrystallization growth process, and the distribution in the longitudinal direction affects the region where the crystal grows. In order to manufacture a thin film transistor having excellent characteristics, an appropriate beam profile and irradiation intensity must be selected. However, in the above-described optical system for forming a rectangular beam, the laser output has a limit, and it is necessary to shorten the length of the irradiation laser beam in the longitudinal direction in order to obtain a necessary irradiation intensity, and thus the productivity is low. .

SUMMARY OF THE INVENTION The present invention has been made to solve such a problem. A silicon thin film having a low density of lattice defects and high crystallinity can be formed by laser heat treatment, and the productivity of the silicon thin film can be improved. It is an object of the present invention to provide a laser annealing device having a high laser annealing.

[0013]

A laser annealing apparatus according to the present invention irradiates a laser oscillator, a laser beam emitted from the laser oscillator onto an amorphous or polycrystalline semiconductor film, and emits the irradiated laser beam. A laser optical system for forming a linear shape, and crystallization of the semiconductor film by a linear irradiation laser beam, the apparatus is provided with a plurality of laser optical systems, from each laser optical system on the semiconductor film Each of the irradiated linearly irradiating laser beams is positioned substantially linearly on the surface of the semiconductor film at an arbitrary interval in its length direction. A single sweep can crystallize a plurality of rows of surface areas, improve efficiency, and further provide an interval, so that there is no interference between the linear irradiation laser beams, and a crystal film with few defects can be reliably generated. .

In the laser annealing apparatus of the present invention, preferably, the interval between the linear beams is set substantially equal to or slightly smaller than the width of the linear beam. In particular, when the distance between the linear beams is n, the width of the linear beam w, the distance d between the linear beams, and the width of the area of the substrate to be irradiated with the laser beam is L, w
+ D) × n ≧ L. With such an arrangement of the intervals between the irradiation laser beams, polycrystallization can be performed by irradiating the irradiation laser beams in the second pass toward this interval after the first pass.

The apparatus of the present invention is preferably applied to a silicon film to form a polycrystalline silicon film having uniform and large crystal grains, and is used for forming a high-speed thin film transistor for a pixel portion of a liquid crystal display. It can be used as a substrate.

The laser oscillator operates from 350 nm to 800 n.
It is preferable to emit a laser beam having an oscillation wavelength between m and m, and this wavelength light is preferable in terms of uniform heating in the thickness direction of the silicon film. In particular, a laser oscillator uses a harmonic of a solid-state laser. I do.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1 As shown in FIG. 1, the laser annealing apparatus of this embodiment has three laser oscillators 1a to 1c, linear beam shaping means 3a to 3c as respective laser optical systems, and respective reflecting mirrors 4a to 4c.
c is arranged so that the beam optical axis is substantially horizontal, and each of the reflecting mirrors 4 a to 4 c is arranged above the substrate 50 on the stage 6.

A laser beam 2 (2a to 2c) is emitted from each of the three laser oscillators 1 (1a to 1c) to each linear beam forming means 3 (3a to 3c) as a corresponding laser optical system. In the beam forming means 3a to 3c, the beam is shaped so that the profile of the beam when the silicon film is irradiated is linear. The beam from each linear beam forming means 3 (3a to 3c) is
The light is reflected by (4a to 4c) and irradiated perpendicularly to the surface of the silicon film 5.

The linear beam shaping means 3 respectively irradiates the irradiation laser beams 8a, 8b, 8c on the silicon film on the substrate.
Is shaped into a linear beam. As an example, a waveguide 3 having a facing reflection surface as shown in FIG.
2 and a cylindrical convex lens 33 can be used.

FIG. 5 shows an example of the simplest laser optical system 3. The intensity distribution shaping means 30 has an optical waveguide 32 having a pair of reflecting surfaces 320, 320 which face each other in a tapered shape in the y direction. The beam shape shaping means 31 has an x-direction cylindrical convex lens 33. The laser beam 2 incident on the optical waveguide 32 has a y-directional component
The two convex surfaces are reflected in a multiplex manner between the pair of reflecting surfaces 320 and 320, and are combined into a uniform intensity distribution to form a cylindrical convex lens 33.
And the x-direction component of the other incident beam passes between the reflecting surfaces of the waveguide 32,
The light is focused on the silicon film by the cylindrical convex lens 33. Thus, on the silicon film, the irradiation laser beam is y
It has a long and uniform intensity distribution in the direction and has a narrow linear shape with a sharp intensity distribution in the x direction, and is swept in the x direction, the silicon film is heated and melted, and then cooled. You.

In this embodiment, the irradiation laser beams 8a, 8b, 8c on the silicon film 5 on the substrate are:
They are spaced from each other and are arranged substantially linearly. Linear irradiation laser beam 8 irradiated on silicon film
Since a, 8b, and 8c are swept in the width direction (in the x direction in FIG. 1), irradiation areas 85a, 85b, and 85c that are irradiated with laser on the silicon film are arranged at intervals, and In 85a, 85b, and 85c, crystallization progresses in the process of superheating melting and cooling. On the other hand, the irradiation areas 85a, 85
The gap between 5b and 85c remains uncrystallized, but is swept by the next irradiation laser beams 8a, 8b and 8c, and thereby crystallized.

In this embodiment, a laser beam 2 emitted from a plurality of laser oscillators 1a, 1b, 1c
a, 2b and 2c are simultaneously applied to the semiconductor film on the substrate through the respective linear beam shaping means, so that the respective irradiation laser beams 8a, 8b and 8c maintain the required irradiation intensity while maintaining the required irradiation intensity. The irradiation area can be increased according to the number, and the productivity can be improved. In addition, both the laser oscillator and the beam shaping means can be arranged on the fuselage at an appropriate interval, and mutual interference can be prevented.

The laser oscillator according to the present invention has a wavelength of 330 nm.
Lasers having an oscillation wavelength between 800 nm and 800 nm are more effective. That is, the laser light in this wavelength region has a relatively small absorption coefficient with respect to amorphous silicon, and the laser light is transmitted in the film thickness direction. This can limit the lateral temperature distribution in the silicon film generated by the laser irradiation only in the x direction. Therefore, a portion of the beam having a certain intensity or more in the silicon film on the substrate is uniformly melted in the entire depth direction.

As described above, the thickness direction of the silicon film can be uniformly heated, and the laser heat treatment can form coarse crystal grains in the silicon film, and has excellent crystallinity for forming a thin film transistor having a low lattice defect density. A silicon thin film is obtained.

For such a laser having an oscillation wavelength in the range of 340 nm to 800 nm, a solid-state laser harmonic generation source can be preferably used. Nd: YA for solid state laser
The second harmonic (532 nm) and the third harmonic (3
55 nm), the second harmonic of the Nd: YLF laser (524
nm), the third harmonic (349 nm), or Yb: Y
The second harmonic (515 nm) and the third harmonic (344 nm) of an AG laser can be used. Ti: A fundamental wave or a second harmonic of a sapphire laser may be used. Such a solid-state laser harmonic source is 340 nm
Laser light having an oscillation wavelength between 1 nm and 800 nm can be efficiently obtained with a compact device, and stable operation can be performed for a long time.

On the other hand, the silicon film to be laser treated is
The size and shape are determined according to the application. A glass or ceramic substrate is used as the substrate, and an insulating layer, for example, a silicon oxide film is formed as a base film on the substrate. The silicon oxide film is formed by CVD (Chemical Vapor D)
eposition) method. Its thickness is in the range of 100 to 300 nm, especially 200 nm.
To the extent. The silicon film to be treated is formed on an underlying silicon oxide film, and depending on its use, for example, L
PCVD (Low Pressure Chemical Vapor Deposition)
An amorphous silicon film having a thickness of, for example, 30 to 100 nm, in particular, about 50 nm in thickness is formed by a method. The silicon film may be amorphous or crystalline. Substrate 5 having such a silicon film formed thereon
0 is placed and fixed on the stage.

The linear irradiation laser beam is irradiated on the silicon film while relatively moving in the width direction, that is, in the x direction. For the movement, there are a method of scanning the stage by making the stage movable in two directions with respect to the fixed laser optical system, and a method of repeatedly scanning the laser optical system with the stage fixed.

When the silicon film that is moving relatively is irradiated with the laser beam, the silicon film absorbs the laser beam, is heated, and is melted into a rectangle corresponding to the shape of the laser beam. The melted silicon film has a temperature gradient only in the x direction of the moving direction, and the longitudinal direction of the irradiation laser beam 8, that is, the y direction, has a temperature gradient because the intensity distribution of the irradiation laser beam 8 is uniform. Does not occur. Since the molten silicon film crystallizes and grows along the temperature gradient, it becomes one-dimensional growth (unidirectional growth) in the moving direction of the substrate 50, that is, in the x direction, and the crystal grain size is as large as several μm. It is formed.

The process of crystal growth by irradiation is greatly affected by the temperature distribution formed in the x direction in the amorphous or polycrystalline silicon film. That is, it is greatly affected by the intensity distribution in the width direction of the irradiated rectangular beam. The heat introduced into the amorphous or polycrystalline silicon film by laser light irradiation is uniformly dissipated to the substrate. That is, the temperature distribution in the x direction in the amorphous or polycrystalline silicon film is uniformly reduced. Accordingly, the crystal of the molten silicon film grows from a portion where the temperature has first passed the melting point to a portion where the temperature has dropped below the melting point. The growing crystal is blocked by microcrystals grown by the generation of natural nuclei during the process of lowering the temperature, and the crystal growth in the x direction is stopped. That is, it is necessary that the crystal grains grow as long as possible until the time when spontaneous nucleation occurs. For that purpose, a high crystal growth rate is required.

In general, the crystal growth rate v in a certain minute region depends on the ratio of the temperature difference ΔT in the minute region to the width Δx of the minute region, that is, v = kΔT /
It is represented by Δx. Here, k is a rate constant.

That is, when there is a temperature distribution in the x direction in the silicon film, the crystal growth rate can be increased if the temperature gradient in the region having a temperature equal to or higher than the melting point is steep, and as a result, the crystal grain size is large. A polycrystalline silicon film can be formed, and a thin film having excellent crystallinity required for manufacturing a high-performance thin film transistor can be formed.

The apparatus shown in the present embodiment also applies the first and second laser beams 2b and 2c emitted from the second laser oscillator 1b and the third laser oscillator 1c to the first laser oscillator 1b.
Similarly to the laser beam 2a, the substrate 50 on which the amorphous or polycrystalline silicon film is formed is irradiated as a linear beam. Thus, the plurality of laser oscillators 1
laser beams 2a, 2a, 2a
By simultaneously irradiating the substrate with b and 2c, the irradiation area can be increased while maintaining the required irradiation intensity, and the productivity can be improved.

When the area required for laser irradiation on the substrate is large, the first to third irradiation laser beams 8a to 8c are provided with a certain interval in the y direction, and Can be arranged substantially linearly. The irradiation laser beams are separated from each other until x
After a predetermined distance on the silicon film surface in the direction,
In the direction, the beam is moved by a distance equal to or slightly smaller than the beam width, and is moved again in the x direction. Laser irradiation is performed on the entire region of the substrate where laser irradiation is necessary. At this time, the amount of movement in the y direction in one pass is smaller than the case where no interval is provided between the irradiation laser beams, and since there is an interval between the irradiation laser beams, a plurality of laser beams such as linear beam forming means are provided. The optical system can also be arranged at a distance, and interference of optical components can be prevented.

Embodiment 2 FIG. 2 is a schematic perspective view of an optical system of the laser annealing device according to the second embodiment.
In this embodiment, the irradiation laser beam interval d is set equal to or slightly smaller than the irradiation laser beam width w. In addition, the structure of the laser optical system and the function of the irradiated laser beam on the amorphous or polycrystalline silicon film are the same as those described in the first embodiment.

According to such an arrangement of the irradiation laser beam, after the first scanning pass, the amount of movement of the silicon film in the y direction is made substantially equal to the irradiation laser beam interval d, and then the substrate is scanned again. The laser beam can be irradiated to the region width L to be irradiated with the laser beam, and uniform heat treatment can be performed.

Embodiment 3 In this embodiment, in FIG. 3, the irradiation laser beam interval d on the silicon film is the irradiation laser beam width w, the irradiation laser beam interval d, the area width L on the substrate to be irradiated with laser light, and the number of irradiation laser beams n
Is set so as to satisfy (w + d) × n ≧ L. Also in this embodiment, the structure of the laser optical system and the function of the irradiated laser beam on the amorphous or polycrystalline silicon film are the same as those described in the first embodiment.

According to the arrangement of the irradiation laser beams, the interval between the laser optical systems of a plurality of beams can be maximized, so that a plurality of laser optical systems such as linear beam forming means can be arranged at a distance, and the optical components Since interference can be prevented and the amount of one movement of the substrate 50 in the y direction can be minimized,
The operation of the y-direction moving mechanism can be stabilized.

[0038]

According to the laser annealing apparatus of the present invention, a plurality of laser beams are used to irradiate a semiconductor film with a plurality of irradiation laser beams at intervals, so that the irradiation area in one pass can be increased. As a result, the productivity of the polycrystalline semiconductor film can be increased, and laser optical systems such as a plurality of linear beam forming means can be arranged at a distance, so that interference of optical components can be prevented.

If the interval between the linear beams is set to be substantially equal to or slightly smaller than the width of the linear beams, the laser beam can be irradiated to the region width L to be irradiated on all the substrates. And a uniform heat treatment can be performed.

The relationship between the number n of the laser beams, the width w of the linear beam, the distance d between the linear beams, and the width of the area of the substrate where the laser beam needs to be irradiated, L, satisfies the relationship (w + d) × n ≧ L. By setting the interval between the linear irradiation laser beams as described above, the interval between the laser optical systems of a plurality of beams can be maximized, so that laser optical systems such as a plurality of linear beam forming means can be arranged at a distance, and the optical Since the interference of components can be prevented and the amount of one-time movement in the y-direction of the substrate 50 on which the amorphous or polycrystalline semiconductor film is formed can be minimized at equal intervals, the operation of the y-direction movement mechanism can be performed. Can be stabilized.

By applying an amorphous silicon film formed on a substrate to a semiconductor film, a polycrystalline semiconductor film can be mass-produced with few lattice defects and used for a liquid crystal display. It can be used as a high performance silicon substrate for thin film transistors.

A laser oscillator of 350 nm to 800 nm
By using an oscillation wavelength in the range, the thickness direction of the amorphous or polycrystalline silicon film can be uniformly heated, and a thin film with excellent crystallinity can be obtained by laser heat treatment. can do.

If the laser oscillator uses harmonics of a solid-state laser, the laser oscillator can be made compact and
The thickness direction of the amorphous or polycrystalline silicon film can be uniformly heated. A thin film having excellent crystallinity required for manufacturing a high-performance thin film transistor by a laser heat treatment method can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic perspective view of a laser annealing device according to an embodiment of the present invention.

FIG. 2 is a schematic perspective view of a laser annealing device according to another embodiment of the present invention.

FIG. 3 is a schematic perspective view showing an arrangement of a laser annealing device according to another embodiment of the present invention.

FIG. 4 shows a laser optical system for laser heat treatment which forms the basis of the laser annealing apparatus of the present invention.

FIG. 5 shows the structure of a laser optical system for laser heat treatment.

[Explanation of symbols]

1 laser oscillator, 2 laser beams, 3a, 3b, 3
c Linear beam forming means, 5 silicon film, 51 base film, 50 substrate, 6 moving stage.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Yukio Sato 2-3-2 Marunouchi, Chiyoda-ku, Tokyo Mitsui Electric Co., Ltd. (72) Inventor Junichi Nishimae 2-3-2 Marunouchi, Chiyoda-ku, Tokyo F term (reference) in Mitsubishi Electric Corporation 5F052 AA02 BA07 BA14 BB02 BB07 CA10 DA01 DA02 DB02 JA01 5F110 DD13 GG02 GG13 GG15 GG44 PP04 PP07

Claims (6)

[Claims] 1. A laser oscillator comprising: a laser oscillator; and a laser optical system that irradiates a laser beam emitted from the laser oscillator onto an amorphous or polycrystalline semiconductor film and forms the irradiated laser beam into a linear shape. A laser annealing apparatus for crystallizing a semiconductor film by a linear irradiation laser beam, wherein a plurality of laser optical systems are arranged in the apparatus, and each linear irradiation laser irradiated on the semiconductor film from each laser optical system. A laser annealing apparatus characterized in that beams are arranged substantially linearly on the surface of a semiconductor film at arbitrary intervals in the longitudinal direction thereof. 2. The laser annealing according to claim 1, wherein the distance between the linear irradiation laser beams on the silicon film is substantially equal to or slightly smaller than the length of the linear irradiation laser beam. apparatus. 3. The distance d between the linear beams is (w + d) × n, where n is the number of laser beams, w is the width of the linear beams, and L is the width of the region of the substrate to be irradiated with laser light. The laser annealing apparatus according to claim 1, wherein the laser annealing apparatus is set so as to satisfy a relationship of? L. 4. The laser annealing apparatus according to claim 1, wherein the semiconductor film is an amorphous silicon film formed on a substrate. 5. The laser annealing apparatus according to claim 1, wherein the laser oscillator is a pulse laser oscillator having an oscillation wavelength of 330 to 800 nm. 6. The laser annealing apparatus according to claim 5, wherein the laser oscillator uses a harmonic of a solid-state laser.